The present invention relates to systems for inductively heating fluid-carrying conduits. In another aspect, the invention relates to a system for inductively heating a submarine petroleum pipeline by using at least one electrical cable that can also provide power to an off-shore petroleum production platform.
Petroleum produced from off-shore reservoirs is typically transported from one or more off-shore production facilities through submarine pipelines to a central facility for processing. Such off-shore production facilities require electrical power for operation. The central processing facility, which may be on-shore or off-shore, usually includes petroleum processing equipment and electrical power generating equipment. The electrical power generated at the central facility is commonly transmitted to the off-shore production facilities through submarine electrical cables running adjacent the submarine transportation pipeline.
When the submarine petroleum pipeline is surrounded by cool water, the unprocessed well stream (e.g., a multiphase mixture comprising oil, gas, and water) transported in the pipeline is at a risk of increasing in viscosity to a point where it cannot be pumped through the terminal end of the pipeline. For example, if the flow of the well stream is stopped, the well stream cools rapidly and increases in viscosity. If the well stream cools below a certain temperature (e.g., 20xc2x0 C.), crystallization and hydrate development render the well stream too viscous to be pumped through the terminal end of the pipeline.
One method known in the art for regulating the viscosity of the well stream in the pipeline is to insulate and electrically heat the pipeline. Prior art methods of electrically heating the pipeline include the use of an in-pipeline heating cable, impedance heating wherein the steel pipeline is used as an electric resistance element, and induction heating using either skin effect current tracing, dedicated supply conductors, and/or dedicated return conductors. These prior art methods are problematic and have several limitations. For example, in-pipeline heating cables, impedance heating, and skin effect induction heating are not equipped to reliably heat longer pipelines requiring a construction utilizing numerous joints. In addition the prior art methods of electrically heating the pipeline either require equipment that is incapable of also being used for electrical power transmission or require the installation of additional submarine cables in order to function. These limitations are undesirable and result in increased installation costs of either duplicate systems for heating and power transmission or multiple submarine cables. Moreover, existing off-shore electrical power transmission systems can not be efficiently and cost-effectively converted into pipeline heating systems using prior art methods.
It is an object of the present invention to provide an inductive heating system which, when not being used for heating, can also be used to transmit conventional electrical power.
A further object of this invention is to provide an inductive heating system for a submarine pipeline which is less expensive to install than prior art pipeline heating systems.
It is yet another object of the present invention to provide an inductive heating system for a submarine pipeline which employs a conventional submarine power cable as the heat inducing element.
It is still another object of the present invention to provide an inductive heating system which can be installed and operated in conjunction with an existing submarine petroleum pipeline without placing a new submarine electrical cable along the existing pipeline.
A yet further object of the present invention is to provide an pipeline heating system which can cost-effectively be employed to heat a submarine pipeline of considerable length (i.e., requiring numerous individual pipe sections).
In accordance with one embodiment of the present invention, an apparatus comprising a power source, a powered system, an electrically conductive fluid conduit, an electrical cable positioned proximate the fluid conduit, and a switching device is provided. The cable has a first end which is electrically couplable to the power source and a second end which is electrically couplable to the powered system. The switch is operable to selectively switch electricity conducted through the cable between a heating mode, in which the fluid conduit is inductively heated without providing electricity to the powered system, and a powering mode, in which electricity is provided to the powered system via the cable without substantial inductive heating of the fluid conduit.
In accordance with a further embodiment of the further invention, an apparatus comprising a petroleum pipeline, an electrical cable positioned proximate the pipeline, a powered system electrically couplable to the cable, a first power source, a second power source, and a power source switching device is provided. The first power source is operable to provide electricity in a powering mode to the powered system via the cable. Substantially no inductive heating of the pipeline is provided by the electricity in the powering mode. The second power source is operable to provide electricity in a heating mode to the cable. The electricity in the heating mode provides inductive heating of the pipeline. The power source switching device is operable to selectively switch the apparatus between the powering mode and the heating mode.
In yet another embodiment of the present invention, an apparatus comprising a submarine petroleum pipeline, a first electrical cable, a second electrical cable, a powered system, a first power source, a second power source, and at least one electrical switching device is provided. The first and second electrical cables are positioned proximate and extend generally parallel to the pipeline. The powered system is electrically couplable to the first and second electrical cables. The first power source provides electricity to the powered system via the first and second electrical cables when the apparatus is operated in a powering mode. The second power source provides electricity to the first and second electrical cables when the apparatus is operated in a heating mode. When the apparatus is operated in the heating mode, the first and second electrical cables are electrically decoupled from the powered system. The electrical switching device is operable to selectively switch the apparatus between the powering mode and the heating mode.
In still another embodiment of the present invention, an apparatus comprising an electrically conductive fluid conduit, at least one power source, a powered system, an electrical cable, and means for selectively altering electricity is provided. The electrical cable is positioned proximate the fluid conduit and is electrically couplable to the power source and the powered system. The means for selectively altering electricity is operable to selectively alter electricity conducted to the cable between a heating mode in which the fluid conduit is inductively heated without providing electricity to the powered system and a powering mode in which electricity is provided to the powered system without substantial inductive heating of the fluid conduit.
In another embodiment of the present invention, a method of heating an electrically conductive fluid conduit is provided. The method comprises the steps of: (a) positioning an electrical cable proximate the electrically conductive fluid conduit; (b) conducting electricity in a powering mode to the cable, wherein the electricity in the powering mode provides substantially no inductive heating of the fluid conduit; and (c) conducting electricity in a heating mode to the cable, wherein the electricity in the heating mode inductively heats the fluid conduit.
In a yet further embodiment of the present invention, a method of heating a submarine pipeline using a submarine electrical cable is provided. The method comprises the steps of: (a) positioning the cable proximate the pipeline: (b) electrically coupling the cable to a first power source and a powered system; (c) conducting electricity in a powering mode from the first power source to the powered system via the cable; (d) electrically decoupling the cable from the powered system; and (e) while said cable is electrically decoupled from said powered system, conducting electricity in a heating mode to the cable to thereby inductively heat the pipeline.
In a still further embodiment of the present invention, a method of providing heat to a submarine petroleum pipeline having a power cable positioned proximate thereto, with the power cable operable to conduct electrical power from a first power supply to a powered wellhead system is provided. The method comprises the steps of: (a) providing a second power supply; and (b) providing a power source switching device operably to selectively switch the power cable between a powering mode in which the power cable is electrically coupled to the first power supply and a heating mode in which the power cable is electrically coupled to the second power supply.
It should be noted that the above-listed objects need not all be accomplished by the invention claimed herein and other aspects and advantages of the present invention will be apparent from the following detailed description of the invention, the appended claims, and the accompanying drawing figures.